The structure of conventional fan wheel is shown in FIG. 9. The fan wheel has a hollow hub 4. A connecting part 41 is arranged in the bottom of the hollow hub 4, having a side extend to at least one blade 42. At least one perforation 43 is disposed between the hollow hub 4 and the blade 42 on the surface of the connecting part 41. Thus, a fan wheel is formed.
Although the fan wheel mentioned above can be fabricated in a fan case (not shown) in order to guide airflow, however, since both the top side of the hollow hub 4 and joint portion between the bottom side of the hollow hub 4 and the connecting part 41 are in a foursquare shape, when airflow blows from the top side of the hollow hub 4 toward the blades 42, no guiding structure is provided from the structure of the fan wheel. Therefore, the airflow entering into the top side of the hollow hub 4 will generate turbulence (as shown in FIG. 10), resulting in difficulty in outputting the air. Thus, it results in more power consumption and further worsens the performance. Since at least one perforation 43 is disposed on the surface of the connecting part 41 between the hollow hub 4 and blades 42, when airflow enters from the top side of the hollow hub 4 and blows toward the blades 42, in addition to the generated turbulence which results in airflow reduction, some part of airflow will blow out from the perforation 43 without being guided to the blades 42. Furthermore, airflow will generate considerable operation noise due to the perforation 43.
Furthermore, another prior art in the U.S. Pat. No. 2003/0143070A1 comprises:
a first set of blades composed of a plurality of blades;
a second set of blades composed of a plurality of blades; and
a plurality of sliding portion, respectively connecting to each blades between said first set of blades and said second set of blades.
Although in the above U.S. Patent, the sliding portion between the first set of blades and the second set of blades is used to guide airflow, since it merely adds one sliding portion in the blades without reforming the whole guiding structure of the fan wheel, the guiding efficacy of the sliding portion is restricted and is insufficient to meet user's needs.